White Spots / Powdery Mildew: Causes, Diagnosis & Fixes
White powdery patches on leaves are typically caused by powdery mildew, a common fungal issue. Other white spots may be mineral deposits or pest related.
Quick diagnosis
Distinguish between fungal mildew, mineral deposits, and pests before treating. Improved air circulation is the best preventive measure.
考えられる原因
Powdery Mildew Fungus
Why: Thrives in warm, humid conditions with poor air circulation. Spreads via airborne spores.
Signs to check: White powdery coating on leaf surfaces, starts in patches and spreads, leaves may distort.
Hard Water Deposits
Why: Mineral-rich tap water can leave white crusty spots on leaves after misting or overhead watering.
Signs to check: Spots are crusty rather than powdery, appear where water droplets dried, can be wiped off.
Mealybug Residue
Why: Mealybugs produce white, cottony masses that can be mistaken for mildew.
Signs to check: White fluff concentrated at leaf joints and stem bases, sticky residue present.
確認ポイント
- 1Try wiping the white substance — does it come off easily?
- 2Check if the coating is powdery (mildew) or crusty (mineral)
- 3Inspect for cottony clusters and sticky residue (mealybugs)
- 4Assess air circulation around the plant
対処法
- Improve air circulation by spacing plants apart or using a fan
- Remove heavily affected leaves and dispose of them
- Avoid overhead watering and misting affected plants
- Apply a baking soda solution (1 tsp per quart of water) as a mild fungicide
- Use filtered water for misting to prevent mineral deposits
専門家に相談するタイミング
- Mildew is spreading rapidly to other plants
- Leaves are yellowing, distorting, or dying beneath the coating
- Plant is losing vigor despite treatment
ポイント
Distinguish between fungal mildew, mineral deposits, and pests before treating. Improved air circulation is the best preventive measure.
Frequently asked questions
What causes white spots / powdery mildew in houseplants?
White powdery patches on leaves are typically caused by powdery mildew, a common fungal issue. Other white spots may be mineral deposits or pest related. Common causes include powdery mildew fungus, hard water deposits, mealybug residue.
How do I fix white spots / powdery mildew?
Start by identifying the likely cause instead of applying every remedy at once. Improve air circulation by spacing plants apart or using a fan Remove heavily affected leaves and dispose of them Avoid overhead watering and misting affected plants
Track the problem over time
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Sources and review
Content last reviewed: September 4, 2026
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